The invention relates to a combustion engine having at least one outlet passage for explusion of burned gases, terminating at the outside surface of the engine and communicating with an exhaust pipe attached to the outside surface by means of a flange and an intervening gasket, the outlet passage being provided with a tubular liner forming an annular cavity together with the wall of the outlet passage.
It is generally known that in an internal combustion engine, after a cold start and when idling, if the walls of the outlet passage and the adjoining exhaust pipe are comparatively cold, an especially high proportion of injurious constituents will remain in the exhaust. A combustion engine of the type described has therefore been proposed in which the tubular liner arranged in the outlet passage serves the purpose of reducing the proportions of injurious constituents in the exhaust gases even immediately after a cold start, that is, before the outlet passage and the adjoining exhaust pipe have themselves been sufficiently heated. For this purpose, the liner consists of thin-walled refractory material that, unlike the wall of the outlet passage, will be heated very rapidly by the exhaust gases flowing past, and thus contribute to rapid combustion of injurious constituents. Through the attachment of the flanged liner between the outer surface of the engine and the flange of the adjoining exhaust pipe, it is true, there may be undesirable conduction of heat away from the liner heated by the exhaust to colder parts of the engine, and this may furthermore adversely affect the life of the intervening gasket sealing the flange.